clk: qcom: Select QCOM_GDSC with MSM_GCC_8998

If QCOM_GDSC is disabled, gdsc_register() returns -ENOSYS, which causes
gcc_msm8998_probe() to fail. Select QCOM_GDSC to solve the problem.

gcc-msm8998: probe of 100000.clock-controller failed with error -38

Signed-off-by: Marc Gonzalez <marc.w.gonzalez@free.fr>
Fixes: b5f5f525 ("clk: qcom: Add MSM8998 Global Clock Control (GCC) driver")
Signed-off-by: Stephen Boyd <sboyd@kernel.org>